Apparatus and method for eliminating outband interference signal

ABSTRACT

Provided is an apparatus and method for eliminating an outband interference signal. An apparatus for eliminating an interference signal includes a first mixer, a filter unit, a second mixer, and an operation unit. The first mixer downconverts a received signal containing an outband interference signal. The filter unit extracts the downconverted outband interference signal from the downconverted received signal. The second mixer upconverts the downconverted outband interference signal to restore the outband interference signal to the original frequency band. The operation unit subtracts and eliminates the restored outband interference signal from the received signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. §119(a) of a KoreanPatent Application No. 10-2008-0090843, filed on Sep. 6, 2008 in theKorean Intellectual Property Office, the disclosure of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The following disclosure relates to a technology for eliminating aninterference signal from a received signal, and in particular, to anapparatus and method for eliminating an outband interference signal,which may enhance receiving (RX) sensitivity while eliminating aninterference signal from a received signal.

BACKGROUND

Researches have been conducted to provide a multi-band, low-power,one-chip solution. A variety of wireless communication schemes have beenused where each wireless communication receiver is additionally providedwith a block capable of rejecting an interference signal due to otherwireless communication.

A low noise amplifier (LNA) of a wireless communication receiverprovides a high gain for sufficiently amplifying a weak signal input toan antenna. However, where an outband interference signal is inputted inthe LNA, the linearity of the LNA's amplification may degrade.Therefore, it is desirable to eliminate an outband interference signalfrom a front end of the LNA.

A band pass filter (BPF) or a surface acoustic wave (SAW) filter may beused in an outband interference signal elimination method. Because it isdifficult to product a high-Q (Quality factor) inductor necessary to usea sharp BPF, many wireless communication receivers use a SAW filter.

However, the use of a SAW filter may increase the implementation costfor a multi-band mode, and may cause a limitation in sharing a LNA formulti-band or multi-mode applications. Also, a SAW filter may cause aninsertion loss of, for example, about 3 dB, thus degrading the RXsensitivity.

SUMMARY

According to an aspect, there is provided an apparatus and method foreliminating an outband interference signal, which may eliminate anoutband interference signal without using a SAW filter.

According to another aspect, there is provided an apparatus and methodfor eliminating an outband interference signal, which may enhance the RXsensitivity due to a small insertion loss.

According to still another aspect, there is provided an apparatus foreliminating an interference signal, including a first mixerdownconverting a received signal containing an outband interferencesignal, a filter unit extracting the downconverted outband interferencesignal from the downconverted received signal, a second mixerupconverting the downconverted outband interference signal to restorethe outband interference signal to the original frequency band, and anoperation unit subtracting and eliminating the restored outbandinterference signal from the received signal.

According to yet another aspect, there is provided an apparatus foreliminating an interference signal, including a balun transformerdividing a received signal containing an outband interference signalinto a first signal and a second signal that are identical to eachother, a first mixer downconverting the first signal and the secondsignal, a filter unit extracting the downconverted outband interferencesignals from the downconverted first signal and the downconverted secondsignal, a second mixer upconverting the extracted outband interferencesignals to restore the outband interference signals to the originalfrequency band, and an operation unit subtracting the restored outbandinterference signals from the first signal and the second signal.

According to yet another aspect, there is provided an apparatus foreliminating an interference signal, including a first mixerdownconverting a received signal containing an outband interferencesignal, a filter unit extracting the downconverted outband interferencesignal from the downconverted received signal, a second mixerupconverting the downconverted outband interference signal to restorethe outband interference signal to the original frequency band, anoperation unit subtracting and eliminating the restored outbandinterference signal from the received signal, a variable attenuatorcontrolling the amplitude of the outband interference signal before therestored outband interference signal is provided to the operation unit,a delay unit delaying the received signal by a predetermined time inconsideration of the process times of the first mixer, the filter unitand the second mixer and providing the resulting signal to the operationunit, and a low-noise amplifier low-noise-amplifying the received signalwithout the outband interference signal.

According to yet another aspect, there is provided a method foreliminating an interference signal, including downconverting a receivedsignal containing an outband interference signal, extracting thedownconverted outband interference signal from the downconvertedreceived signal, upconverting the downconverted outband interferencesignal to restore the outband interference signal to the originalfrequency band, and eliminating the restored outband interference signalfrom the received signal.

Other features will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theattached drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an apparatus for elimination ofan outband interference signal according to an exemplary embodiment.

FIGS. 2 to 9 are graphs illustrating a frequency-domain spectrum of anapparatus for elimination of an outband interference signal according toan exemplary embodiment.

FIG. 10 is a block diagram illustrating an apparatus for elimination ofoutband interference signal according to another exemplary embodiment.

FIG. 11 is a flow diagram illustrating an outband interference signalelimination method according to an exemplary embodiment.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The elements maybe exaggerated for clarity and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses and/orsystems described herein. Accordingly, various changes, modifications,and equivalents of the systems, apparatuses and/or methods describedherein will be suggested to those of ordinary skill in the art. Also,descriptions of well-known functions and constructions are omitted toincrease clarity and conciseness.

FIG. 1 illustrates an apparatus for elimination of an outbandinterference signal according to an exemplary embodiment. FIGS. 2 to 9are graphs illustrating a frequency-domain spectrum of an apparatus forelimination of an outband interference signal according to an exemplaryembodiment. Hereinafter, the respective components of an apparatus forelimination of an outband interference signal according to an exemplaryembodiment will be described with reference to FIGS. 1 to 9.

Referring to FIG. 1, the apparatus for elimination of an outbandinterference signal outputs a signal {circle around (h)} by eliminatingan outband interference signal from a received signal {circle around(a)}. The apparatus comprises a first mixer 130, a filter unit 140, asecond mixer 150, a delayer 170, and an operation unit 160.

The first mixer 130 outputs a signal {circle around (b)} bydownconverting the received signal {circle around (a)} containing anoutband signal, which is separated by a duplexer 120 after beingreceived through an antenna 110, to a local frequency band. For example,the first mixer 130 downconverts the received signal {circle around (a)}into the signal {circle around (b)} by multiplying the received signal{circle around (a)} by a local-frequency signal LO that is generated bya local frequency generator (not illustrated).

The duplexer 120 separates a transmitting (TX) signal and a receiving(RX) signal by frequency division so that the TX signal and the RXsignal do not collide with each other. Herein, the duplex 120 may bereplaced with a switch that separates a TX signal and an RX signal bytime division so that the TX signal and the RX signal do not collidewith each other.

The filter unit 140 extracts a downconverted outband interference signal{circle around (d)} from the output signal {circle around (b)} of thefirst mixer 130. The filter unit 140 includes a high pass filter (HPF)and a low pass filter (LPF).

For example, the HPF extracts a high-frequency signal {circle around(c)} containing an outband interference signal from the output signal{circle around (b)} of the first mixer 130, and the LPF extracts thedownconverted outband interference signal {circle around (d)} from thesignal {circle around (c)}.

Although FIG. 1 illustrates that the filter unit 140 outputs thedownconverted outband interference signal {circle around (d)} by passingthe signal {circle around (b)} through the HPF and then through the LPF,the filter unit 140 may be configured to output the downconvertedoutband interference signal {circle around (d)} by passing the signal{circle around (b)} through the LPF and then through the HPF.

The second mixer 150 upconverts the downconverted outband interferencesignal {circle around (d)} into an outband interference signal {circlearound (f)} of an original frequency band by multiplying thedownconverted outband interference signal {circle around (d)} by alocal-frequency signal.

The operation unit 160 outputs a signal {circle around (h)} bysubtracting the outband interference signal {circle around (f)} from areceived signal {circle around (g)} delayed by a predetermined time.

Herein, the received signal {circle around (a)}, which is separated by aduplexer 120 after being received through an antenna 110, is dividedinto two identical signals that are provided respectively to the delayer170 and the first mixer 130. The delayer 170 delays the signal {circlearound (a)} by a time taken to perform the operations of the first mixer130, the filter unit 140 and the second mixer 150, and provides theresulting signal {circle around (g)} to the operation unit 160.

Thereafter, the signal {circle around (h)} is low-noise-amplified by alow noise amplifier (LNA) 190 for use in various processes.

The apparatus for elimination of an outband interference signal mayfurther comprise a variable attenuator 200 and a detection unit 210. Bythe calibration on/off control of a microcomputer (not illustrated), thevariable attenuator 200 attenuates the amplitude of the downconvertedoutband interference signal {circle around (d)} and provides theresulting signal {circle around (e)} to the second mixer 150. Thedetection unit 210 controls the amplitude attenuation level of thevariable attenuator 200.

That is, in a calibration-on state, the apparatus controls the setamplitude offset of the variable attenuator 200 and the detection unit210 to compensate a mismatch between a first path and a second path, andoperates the variable attenuator 200 and the detection unit 210 byreceiving the fed-back operation results of the operation unit 160,thereby reducing the residual outband interference signal. In acalibration-off state, the apparatus may compensate only a mismatchbetween the first path and the second path by operating only acalibration block 180 without operating the variable attenuator 200 andthe detection unit 210, or may omit the mismatch compensation by thevariable attenuator 200, the detection unit 210 and the calibrationblock 180.

The detection unit 210 may set an amplitude offset value according to amismatch between the first path including the filter unit 140 and thesecond mixer 150 and the second path including the delayer 170 by usingthe calibration block 180, or may set the amplitude offset value byextraction of the residual outband interference signal by receiving thefed-back output of the operation unit 160. That is, before eliminationof the outband interference signal from the received signal, thedetection unit 210 compensates the mismatch between the first path andthe second path so that the mismatch between the first path and thesecond path does not affect the elimination of the outband interferencesignal from the received signal.

In another embodiment, the detection unit 210 receives the fed-backoutput signal {circle around (h)} of the operation unit 160, detects theresidual outband interference signal, and uses the same for theamplitude control of the variable attenuator 200, and the settings forthe amplitude control of the detection unit 210 may change frequently(e.g., real-timely, periodically or intermittently). In this case, thedetection unit 210 detects the amplitude from the power of the residualoutband interference signal, converts the detected amplitude into ananalog signal, and provides the analog signal to the variable attenuator200, thereby controlling the amplitude of the outband interferencesignal.

Before inputting of the received signal, the calibration block 180outputs a virtual outband interference signal through the oscillation ofan oscillator (not illustrated), detects the mismatch between the firstpath and the second path, and provides the same to the detection unit210. Herein, the virtual outband interference signal of the oscillatormay be a signal of a frequency band that is adjacent to a frequency bandof a transmitter-receiver using an apparatus for elimination of outbandinterference signal.

Unlike the illustration of FIG. 1, the variable attenuator 200 may beprovided to control the amplitude of the output signal {circle around(f)} of the second mixer 150.

Hereinafter, the spectrum of the output/input signals of the respectivecomponents of the apparatus according to an exemplary embodiment will bedescribed with reference to FIGS. 2 to 9.

FIG. 2 illustrates the spectrum of the signal {circle around (a)}, whichis received by the antenna 110, separated by the duplexer 120 or theswitch and then input to the first mixer 130 and the delayer 170. It maybe seen from FIG. 2 that the signal {circle around (a)} contains adesired signal f_(S) and an undesired interference signal f₁.

FIG. 3 illustrates the spectrum of the output signal {circle around (b)}of the first mixer 130. It may be seen from FIG. 3 that the outbandinterference signal f₁ is downconverted into a signal F_(1-L) of a localfrequency band LO.

FIG. 4 illustrates the spectrum of the output signal {circle around (c)}of the HPF of the filter unit 140. It may be seen from FIG. 4 that asignal of a local frequency band below F_(1-L) was eliminated.

FIG. 5 illustrates the spectrum of the output signal {circle around (d)}of the LPF of the filter unit 140. It may be seen from FIG. 5 thatsignals of a local frequency band above F_(1-L) were eliminated.

FIG. 6 illustrates the spectrum of the output signal {circle around (c)}of the variable attenuator 200. It may be seen from FIG. 6 that thesignal {circle around (e)} is not significantly different in shape fromthe signal {circle around (d)}. However, the signal {circle around (e)}is a signal that is compensated the amplitude error by inputting thesignal {circle around (d)} to the variable attenuator 200.

FIG. 7 illustrates the spectrum of the output signal {circle around (f)}of the second mixer 150, which is upconverted into the originalfrequency band of the outband interference signal.

FIG. 8 illustrates the spectrum of the output signal {circle around (g)}of the delayer 170, which is nearly identical to the received signal{circle around (a)} in terms of the frequency spectrum.

FIG. 9 illustrates the spectrum of the signal {circle around (h)}obtained by subtracting the output signal {circle around (f)} of thesecond mixer 150 from the output signal {circle around (g)} of thedelayer 170. It may be seen from FIG. 9 that the outband interferencesignal F₁ was eliminated.

Thereafter, the signal {circle around (h)} is low-noise-amplified by theLNA 190 for use in various processes.

According to an exemplary embodiment described above, an outbandinterference signal may be eliminated from a received signal {circlearound (a)} without using a band pass filter (BPF) or a SAW Filter.

FIG. 10 illustrates an apparatus for elimination an outband interferencesignal according to another exemplary embodiment.

Referring to FIG. 10, the apparatus for elimination of an outbandinterference signal divides a received signal into two signals, detectsan outband interference signal of each of the two signals, andeliminates the outband interference signal from each of the two signals.The apparatus comprises a balance-to-unbalance (balun) transformer 1100,delayers 1170 a and 1170 b, a first mixer 1130, a filter unit 1140, asecond mixer 1150, and operation units 1160 a and 1160 b.

The balun transformer 1100 divides a single-ended received signalcontaining an outband interference signal into differential-ended firstand second signals that are identical to each other.

The first mixer 1130 downconverts the first signal containing an outbandinterference signal and the second signal containing an outbandinterference signal to a local frequency band by multiplying the firstsignal and the second signal by a signal of a local frequency band.

The filter unit 1140 extracts the outband interference signal containedin the downconverted first signal and the outband interference signalcontained in the downconverted second signal.

The second mixer 1150 upconverts the extracted outband interferencesignals to the original frequency band by multiplying the extractedoutband interference signals by a signal of a local frequency band.

The operation unit 1160 a/1160 b outputs the first/second signal withoutan interference signal by subtracting the upconverted outbandinterference signal from the first/second signal delayed by apredetermined time.

Herein, the first and second signals divided by the balun transformer1100 are provided to the delayers 1170 a and 1170 b and the first mixer1130. The delayers 1170 a and 1170 b delay the first and second signalsby a time taken to perform the operations of first mixer 1130, thefilter unit 1140 and the second mixer 1150, and provides the resultingsignals to the operation units 1160 a and 1160 b.

Thereafter, the first and second signals without an outband interferencesignal are low-noise-amplified by a differential low noise amplifier(LNA) 1190 for use in various processes.

The apparatus for elimination of an outband interference signal mayfurther comprise a variable attenuator 1220 and a detection unit 1210.By the calibration on/off control of a microcomputer (not illustrated),before provision of the first and second signals to the operation units1160 a and 1160 b, the variable attenuator 1220 attenuates the amplitudeof the restored outband interference signal and provides the resultingsignal to the second mixer 1150. The detection unit 1210 controls theamplitude attenuation level of the variable attenuator 1220.

That is, in a calibration-on state, the apparatus controls the setamplitude offset of the variable attenuator 1220 and the detection unit1210 to compensate a mismatch between a first path and a second path,and operates the variable attenuator 1220 and the detection unit 1210 byreceiving the fed-back operation results of the operation units 1160 aand 1160 b, thereby reducing the residual outband interference signal.In a calibration-off state, the apparatus may compensate only a mismatchbetween the first path and the second path by operating only acalibration block 1180 without operating the variable attenuator 1220and the detection unit 1210, or may omit the mismatch compensation bythe variable attenuator 1220, the detection unit 1210 and thecalibration block 1180.

The detection unit 1210 may set an amplitude offset value according to amismatch between the first path including the second mixer 1150 and thesecond path including the delayers 1170 a and 1170 b by using thecalibration block 1180, or may set the amplitude offset value byextraction of the residual outband interference signal by receiving thefed-back output of the operation units 1160 a and 1160 b. That is,before elimination of the outband interference signal from the first andsecond signals, the detection unit 1210 compensates the mismatch betweenthe first path and the second path so that the mismatch between thefirst path and the second path does not affect the elimination of theoutband interference signal from the received signal. In anotherembodiment, the detection unit 1210 receives the fed-back output signalsof the operation units 1160 a and 1160 b, detects the residual outbandinterference signal, and uses the same for the amplitude control of thevariable attenuator 1220, and the settings for the amplitude control ofthe detection unit 1210 may change frequently (e.g., real-timely,periodically or intermittently). In this case, the detection unit 1210detects the amplitude from the power of the residual outbandinterference signal, converts the detected amplitude into an analogsignal, and provides the analog signal to the variable attenuator 1220,thereby controlling the amplitude of the outband interference signal.

Before inputting of the received signal, the calibration block 1180outputs a virtual outband interference signal through the oscillation ofan oscillator (not illustrated), detects the mismatch between the firstpath and the second path, and provides the same to the detection unit1210. Herein, the virtual outband interference signal of the oscillatormay be a signal of a frequency band that is adjacent to a frequency bandof a transmitter-receiver using an apparatus for elimination of outbandinterference signal.

Hereinafter, an operation of an apparatus for elimination of an outbandinterference signal according to an exemplary embodiment will bedescribed with reference to FIG. 11.

FIG. 11 is a flow diagram illustrating an outband interference signalelimination method according to an exemplary embodiment.

Referring to FIG. 11, in operation S1110, the apparatus downconverts areceived signal containing an outband interference signal by using alocal frequency signal.

In operation 1120, the apparatus detects a downconverted outbandinterference signal from the downconverted received signal. Herein, theapparatus extracts the downconverted outband interference signal byfiltering the received signal using a HPF and a LPF.

In operation 1130, the apparatus upconverts the downconverted outbandinterference signal to the original frequency band.

In operation 1140, the apparatus eliminates the outband interferencesignal from the received signal by operating the received signal and theupconverted outband interference signal.

Herein, the received signal of the operation S1140 may delayed by a timetaken to perform the operations S1110 to S1130.

The embodiment of FIG. 10 is similar to the embodiment of FIG. 1 withthe exception that, for example, the balun transformer 1100 divides thereceived signal into two identical signals and the signal without anoutband interference signal is input to the differential LNA 1190.

The methods described above may be recorded, stored, or fixed in one ormore computer-readable media that includes program instructions to beimplemented by a computer to cause a processor to execute or perform theprogram instructions. The media may also include, alone or incombination with the program instructions, data files, data structures,and the like. Examples of computer-readable media include magneticmedia, such as hard disks, floppy disks, and magnetic tape; opticalmedia such as CD ROM disks and DVDs; magneto-optical media, such asoptical disks; and hardware devices that are specially configured tostore and perform program instructions, such as read-only memory (ROM),random access memory (RAM), flash memory, and the like. Examples ofprogram instructions include both machine code, such as produced by acompiler, and files containing higher level code that may be executed bythe computer using an interpreter. The described hardware devices may beconfigured to act as one or more software modules in order to performthe operations and methods described above.

According to certain embodiments described above, a miniaturizedone-chip structure may be obtained. Also, the use of certain exemplaryembodiments may enhance the RX sensitivity due to a small insertion losswhile eliminating an outband interference signal.

A number of exemplary embodiments have been described above.Nevertheless, it will be understood that various modifications may bemade. For example, suitable results may be achieved if the describedtechniques are performed in a different order and/or if components in adescribed system, architecture, device, or circuit are combined in adifferent manner and/or replaced or supplemented by other components ortheir equivalents. Accordingly, other implementations are within thescope of the following claims.

1. An apparatus for eliminating an interference signal, comprising: afirst mixer downconverting a received signal containing an outbandinterference signal; a filter unit extracting the downconverted outbandinterference signal from the downconverted received signal; a secondmixer upconverting the downconverted outband interference signal torestore the outband interference signal to the original frequency band;an operation unit subtracting and eliminating the restored outbandinterference signal from the received signal; and a delay unit delayingthe received signal by a predetermined time in consideration of theprocess times of the first mixer, the filter unit and the second mixerand providing the resulting signal to the operation unit.
 2. Theapparatus of claim 1, further comprising a variable attenuatorcontrolling the amplitude of the outband interference signal before therestored outband interference signal is provided to the operation unit.3. The apparatus of claim 1, further comprising a low-noise amplifierlow-noise-amplifying the received signal without the outbandinterference signal.
 4. The apparatus of claim 1, wherein the filterunit comprises: a high-pass filter extracting a high frequency bandsignal containing the outband interference signal from the downconvertedreceived signal; and a low-pass filter extracting a low frequency bandsignal containing the outband interference signal from the extractedhigh frequency band signal.
 5. The apparatus of claim 1, furthercomprising a frequency-division duplexer or a time-division switchextracting the received signal among signals a received antenna.
 6. Anapparatus for eliminating an interference signal, comprising: a firstmixer downconverting a received signal containing an outbandinterference signal; a filter unit extracting the downconverted outbandinterference signal from the downconverted received signal; a secondmixer upconverting the downconverted outband interference signal torestore the outband interference signal to the original frequency band;an operation unit subtracting and eliminating the restored outbandinterference signal from the received signal; a variable attenuatorcontrolling the amplitude of the outband interference signal before therestored outband interference signal is provided to the operation unit;and a detection unit detecting the power of the residual outbandinterference signal according to the subtraction result and providingthe detected power to the variable attenuator, wherein the variableattenuator controls the amplitude of the outband interference signalaccording to the detected power.
 7. An apparatus for eliminating aninterference signal, comprising: a first mixer downconverting a receivedsignal containing an outband interference signal; a filter unitextracting the downconverted outband interference signal from thedownconverted received signal; a second mixer upconverting thedownconverted outband interference signal to restore the outbandinterference signal to the original frequency band; an operation unitsubtracting and eliminating the restored outband interference signalfrom the received signal; a variable attenuator controlling theamplitude of the outband interference signal before the restored outbandinterference signal is provided to the operation unit; a delay unitdelaying the received signal by a predetermined time in consideration ofthe process times of the first mixer, the filter unit and the secondmixer and providing the resulting signal to the operation unit; and alow-noise amplifier low-noise-amplifying the received signal without theoutband interference signal.
 8. The apparatus of claim 7, wherein thefilter unit comprises: a high-pass filter extracting a high frequencyband signal containing the outband interference signal from thedownconverted received signal; and a low-pass filter extracting a lowfrequency band signal containing the outband interference signal fromthe extracted high frequency band signal.
 9. The apparatus of claim 7,further comprising a detection unit detecting the power of the residualoutband interference signal according to the subtraction result andproviding the detected power to the variable attenuator, wherein thevariable attenuator controls the amplitude of the outband interferencesignal according to the detected power.
 10. A method for eliminating aninterference signal, comprising: downconverting a received signalcontaining an outband interference signal; extracting the downconvertedoutband interference signal from the downconverted received signal;upconverting the downconverted outband interference signal to restorethe outband interference signal to the original frequency band;eliminating the restored outband interference signal from the receivedsignal; and delaying the received signal by a time taken to perform thedownconverting of the received signal and the upconverting of theoutband interference signal, wherein the eliminating of the restoredoutband interference comprises subtracting the restored outbandinterference signal from the received signal.
 11. The method of claim10, wherein the extracting of the downconverted outband interferencesignal comprises: extracting a high frequency band signal containing theoutband interference signal from the downconverted received signal; andextracting a low frequency band signal containing the outbandinterference signal from the extracted high frequency band signal. 12.The method of claim 10, wherein the eliminating of the restored outbandinterference signal comprises controlling the amplitude of the restoredoutband interference signal.
 13. The method of claim 10, furthercomprising low-noise-amplifying the received signal without the outbandinterference signal.